Hello. On the basis of the description alone it is not possible to specify the nature of the condition encountered in the case of your quince tree. Strictly concerning the mentioned phenophase (“all petals fallen”), as a preventive measure against the diseases that could then develop, it is recommended to treat with a fungicide such as (which is dissolved in water according to the information on the label and applied by spraying). Subsequently, preventive treatments (fungicides/insecticides) are recommended, depending on the specific phenophase. Information on the optimal application of phytosanitary treatments can be found in our article:: Phytosanitary treatments - environmental and labor protection.
Also, in order to improve the quality of the soil, as well as to provide the necessary nutrients for its growth, it is recommended to use an organic, slow-release fertilizer, such as , as recommended on the label.
More information is provided in the following articles: Quince, planting, growing and harvesting, Quince treatments, pest and disease control.
It is also advisable to check the quince regularly, and if any symptoms appear, please send a message with photos.